In this tutorial I’m demonstrating how to use MQ-2/MQ-5 gas sensors with Arduino. These little devices may be used in gas leakage detectors.
The MQ-2 is suitable for detecting LPG, i-butane, propane, methane, hydrogen and even smoke.
The MQ-5 detects LPG, natural gas and town gas.

Many other gas sensors can be used in exactly the same way, e.g. MQ-3, MQ-6 or MQ-135. Just read the datasheet, use the appropriate load resistor and experiment with the “sensorValue” in my Arduino code.